#include <stdio.h>

int reb(int year);

int main(void)
{
    int year;
    scanf("%d", &year);

    printf("%d年的数量：%d\n", year, reb(year));
    return 0;
}

int reb(int year) {
    return year <= 3 ? 1 : reb(year - 1) + reb(year - 3);
}
